A wide variety of types of sensors are utilized to measure ambient air conditions such as gas concentrations and relative humidity levels. A capacitive sensor is one known sensor type for measuring gas or humidity concentrations (or other analytes as sensors are not limited to gas and humidity). FIG. 1 illustrates one known technique for forming a capacitive sensor 100. As shown in the FIG. 1 cross-section, sensor electrodes 102, 104 and 106 may be formed on a substrate 101 to form the “fingers” of an interdigitated capacitive structure. It will be recognized that the capacitive structure may be formed by many electrodes arranged as shown in FIG. 1. Capacitance measurements obtained between the electrodes may be utilized to determine gas or relative humidity levels. Sensor electrodes may be any of a wide variety of conductive materials. Substrate 101 may be any of a wide variety of substrates and may be in one non-limiting example a semiconductor substrate that includes a wide variety of integrated circuit layers (not shown) as is known in the art. For example, U.S. Pat. No. 8,007,167 to Cummins, the disclosure of which is expressly incorporated herein by reference, provides a capacitive sensor formed on an integrated circuit substrate. The sensor electrodes may be covered by a passivation layer 103 and further overlayed with a sensing layer 105. Alternatively, sensing layer 105 may be utilized without the inclusion of a passivation layer 103. In operation, the sensing layer 105 is exposed to the ambient conditions under which a measurement is desired. Thus, at least a portion of the upper surface of the sensing layer 105 may be an air/dielectric layer interface and layer 105 may be considered an ambient condition sensitive layer. Typically the concentration in the ambient air of the analyte being measured impacts the dielectric constant of the sensing layer as differing concentrations in the ambient air will impact the amount of ingress of the analyte into the sensor dielectric material. By measuring the capacitance between the electrodes the gas or relative humidity concentrations in the ambient air may be inferred. As shown in FIG. 1, the electric fields between the electrodes may include fields 110a contained in the passivation layer 103, fields 110b which pass in part through the sensing layer 105, and other parasitic fields (not shown). In operation, the changes in the dielectric constant of the sensing layer are the changes utilized to detect the ambient gas or relative humidity conditions. However, all of the various components of the capacitive measurement may be impacted by temperature changes, chemical contaminants, physical contaminants, etc., thus impacting the accuracy of the detection of the ambient conditions.
It would be desirable to provide an improved capacitive sensor structure and method of utilizing such structures.
Capacitive sensors are typically provided in a package with an opening defined in the package that is provided for allowing ingress of ambient air or other gas into the package. Such open packages do not provide the same level of protection from the environment for the enclosed circuitry as do conventional closed package configurations that contain other types of circuitry.